docs: def get_session_key(self, username, password_hash):
          """
          Retrieve a session key with a username and a md5 hash of the user's
          password.
          """
  
          params = {"username": username, "authToken": md5(username + password_hash)}
          request = _Request(self.network, "auth.getMobileSession", params)
  
          # default action is that a request is signed only when
          # a session key is provided.
          request.sign_it()
  
          doc = request.execute()
  
          return _extract(doc, "key")